1. Field of the Invention
The present invention relates to a stage apparatus used in a semiconductor exposure apparatus or a testing apparatus, for positioning an object to be exposed, a mask having an original pattern to be transferred, or an object to be tested, to a desired position. The present invention also relates to an exposure apparatus using such a stage apparatus and to a method of producing a device using such an exposure apparatus.
2. Description of the Related Art
Steppers and scanners are widely used as exposure apparatuses in the production of semiconductor devices. A stepper is an apparatus for projecting an image of a pattern formed on a reticle onto a wafer via a projection lens so as to form an image of the pattern with a reduced size on the wafer while moving, in a step-by-step fashion, the semiconductor wafer placed on a stage apparatus and below the projection lens, thereby exposing the wafer shot by shot. In a scanner, on the other hand, a semiconductor wafer placed on a wafer stage and a reticle placed on a reticle stage are moved relative to a projection lens, and exposure light in the form of a slit is emitted when the wafer and the reticle are being moved and scanned so as to project a reticle pattern onto the wafer. The steppers and scanners are widely used as exposure apparatuses because of their high performance in terms of the resolution and registration accuracy.
FIG. 5 illustrates an example of a conventional exposure apparatus. As shown in FIG. 5, the exposure apparatus is constructed on a base frame 1 installed on a floor of a factory. A lens barrel base 2 is supported on the base frame 1. A reduction optical system 3, a reticle stage 4 on which a reticle including an original pattern to be transferred is placed, and an alignment optical system (not shown) are disposed on the lens barrel base 2. In order to avoid the influence of vibrations of the floor on which the apparatus is installed, the lens barrel base 2 is placed on a vibration isolating mechanism 5 using an air spring or the like. In the case of an exposure apparatus of the stepper type, the reticle stage 4 is driven within a small range. In contrast, in the case of an exposure apparatus of the scanner type, the reticle stage 4 is scanned in synchronization with the scanning of a wafer stage 6 which will be described later.
A wafer stage base 7 serving as a guide for horizontally guiding the wafer stage 6 is disposed on the base frame 1. The wafer stage 6 is made up of two stages which can be moved in two directions (X and Y directions) perpendicular to each other so as to carry a wafer in a horizontal plane. More specifically, the wafer stage 6 is made up of a Y stage movable in the Y direction and an X stage which is disposed on the Y stage and which is movable in the X direction. Hydrostatic bearings are disposed between the wafer stage base 7 and the X and Y stages and between the X stage and the Y stage such that the X and Y stages can move with very low friction in the intended moving directions but such that they are supported very rigidly in the direction perpendicular to the moving plane. Therefore, when the Y stage is driven, the X stage moves together with the Y stage. A magnet serving as a mover of a linear motor is disposed on the Y stage, and a stator (in the form of a coil) of the linear motor is disposed on the stage base 7 so that the Y stage is driven by a force generated between the mover and the stator of the linear motor. Similarly, a mover of a linear motor is disposed on the X stage, and a stator of the linear motor is disposed on the Y stage such that a driving force is generated between the mover and the stator. The reaction force of the driving force applied to the X stage acts upon the Y stage and is received by the guide formed on the stage base 7, and thus the X stage is driven in the X direction with respect to the stage base 7.
A fine adjustment stage 8, capable of finely adjusting the position in a rotational direction in the XY plane, in a direction normal to the XY plane, in a rotational direction about the X axis, and in a rotational direction about the Y axis, is disposed on the X stage (the fine adjustment stage 8 will not be described in further detail herein). A wafer to be exposed is placed on a wafer chuck (not shown) on the fine adjustment stage 8. The position of the wafer stage 6 is measured using a high-resolution laser interferometer. In order to achieve high precision positioning of the wafer stage 6, a stage control system is used although it is not shown in FIG. 5. On the basis of the target value of the wafer stage position generated by a main controller (not shown) and the wafer stage position measured by the laser interferometer, the stage control system sends a drive command signal to an actuator of the wafer stage 6. In accordance with the drive command signal, the respective linear motors of the wafer stage 6 are driven by linear motor driving amplifiers (not shown) and generate driving forces in particular directions.
One measure of the performance of the exposure apparatus is the number of wafers which can be handled per unit time (throughput). The wafer stage 6 is moved when a wafer is exchanged, alignment (positioning of the wafer with respect to the exposure optical system) is performed, and the wafer is moved such that each shot area (area to be exposed) of the wafer comes to an exposure position. The moving time of the wafer stage 6 has a large ratio to the total time required to process one wafer. Therefore, to increase the throughput, it is necessary to reduce the time required to move the wafer stage 6 in the X and Y directions. In order to quickly move the wafer stage, it is necessary not only to increase the moving speed but also to quickly perform the acceleration and deceleration. The driving force of the wafer stage 6 is given by the product of the mass of the wafer stage 6 and the acceleration exerted thereon. The reaction force of the driving force applied to the Y stage is transmitted to the base frame 1 via the stage base 7 and further to the floor. The reaction force of the driving force applied to the X stage is transmitted to the base frame 1 via the stage base 7 and further to the floor. If the reaction forces of the driving forces applied to the X and Y stages are great, the base frame 1 and the floor are vibrated. The vibration of the base frame 1 or the floor causes degradation in the positioning accuracy of the wafer stage 6. Besides, because the performance of the vibration isolating mechanism is limited, the vibration is also transmitted to the lens barrel base 2, and the exposure accuracy is degraded. Furthermore, the vibration of the floor exerts an influence upon other apparatus installed at nearby locations.
One known technique to avoid the transmission of the reaction force of the stage driving force to the base frame 1 and the floor is shown in FIG. 6. In this technique, a base 9 is disposed upon a floor such that the base 9 is allowed to freely move in a horizontal direction, and a stage 10 is supported on the base 9 such that the stage 10 is allowed to freely move in the horizontal direction. If a driving force f is applied between the base 9 and the stage 10, an acceleration of xcex1=f/m is exerted upon the stage 10, and an acceleration of xcex2=f/M is exerted upon the base 9 in a direction opposite to the direction in which the stage 10 is accelerated, where m is the mass of the stage 10 and M is the mass of the base 9. That is, in response to accelerations inversely proportional to the masses applied to the stage 10 and the base 9, the stage 10 and the base 9 are moved. However, the reaction forces of the driving force result in the accelerations, and they are cancelled and are not transmitted to the floor.
In the system shown in FIG. 6, because the motion of the stage 10 always occurs with respect to the base 9, the position of the stage 10 with respect to a position measurement reference (floor, for example) disposed in the outside of the system must have a particular relation with the relative position between the stage 10 and the base 9. That is, when displacements are measured with respect to the measurement reference 11 as shown in FIG. 7, the displacement Ys of the Y stage 10 in the Y direction and the displacement Yb of the base 9 in the Y direction must always satisfy equation 3 described below.
Yb=xe2x88x92m/Mxc2x7Ysxe2x80x83xe2x80x83(3)
However, equation (3) holds only under ideal conditions, and it will easily break. The stage 10 can be easily positioned at a desired position by means of feedback control on the basis of a position measurement signal of a measurement system. However, the base 9 moves in a completely passive manner, and it moves only by the reaction force of the driving force applied to the stage 10.
As described below, the stage base system can encounter disturbances which can cause a deviation from equation (3). Ideally, the base 9 is supported by a guide such that the base 9 is allowed to freely move over a floor in a horizontal direction. In practice, however, the guide produces friction which varies depending upon the moving direction. Furthermore, wires of the driving coil or the like act as springs. Moreover, the floor on which the base 9 is supported is not necessarily formed in a perfect horizontal plane. Even if the inclination of the floor is not so large that the base 9 is displaced toward a lower position on the floor when the stage 10 is at rest, the inclination of the floor can cause the base 9 to move by different distances depending upon the direction in which the stage 10 moves. When the stage 10 moves at low velocities with a small acceleration, if the reaction force of the driving force applied to the stage 10 is smaller than the static friction of the base 9, the base 9 is not moved at all. Therefore, if the stage 10 is driven repeatedly at such low velocities, the relative position between the stage 10 and the base 9 deviates from that which satisfies equation (3). In an extreme case, the stage 10 and the base 9 come to positions shown in FIG. 8, and the stage 10 becomes unable to further move in the positive Y direction.
In view of the above, it is an object of the present invention to provide a stage apparatus which always satisfies equation (3) and which exerts a reaction force upon a floor or the like. It is another object of the present invention to provide a stage apparatus characterized in that a moving stage can be moved to any desired position within an allowed range while maintaining a predetermined positional relationship between the moving stage and a stage base. It is still another object of the present invention to provide an exposure apparatus using such a stage apparatus. It is still another object of the present invention to provide a method of producing a device using such an exposure apparatus.
According to a first aspect of the present invention, there is provided a stage apparatus including a first movable member movable in a direction parallel to a reference plane; a second movable member movable in a direction parallel to the reference plane; a first actuator for generating a force between the first movable member and the second movable member; a second actuator for generating a force between the reference plane and the second movable member; a first control system for controlling the position of the first movable member, using the first actuator; and a second control system for controlling the position of the second movable member, using the second actuator in synchronization with the control of the first control system.
In this stage apparatus according to the present invention, when the mass of the first movable member is denoted by m, a target value of the position of the first movable member controlled by the first control system is denoted by Ys, the mass of the the second movable member is denoted by M, and a target value of the position of the second movable member is denoted by Yb, the following relationship preferably holds:
Yb=xe2x88x92m/Mxc2x7Ys.
Preferably, the stage apparatus further comprises an initial position actuator for moving the first movable member and the second movable member to their initial positions.
The initial position actuator may perform the moving to the initial positions by moving the first movable member while maintaining the second movable member at a fixed position.
The stage apparatus may further include a first position measurement system for measuring the position of the first movable member and a second position measurement system for measuring the position of the second movable member.
The first control system may control the position of the first movable member on the basis of the result of the measurement performed by the first position measurement system and also on the basis of the target value of the position, and the second control system may control the position of the second movable member on the basis of the result of the measurement performed by the second position measurement system and also on the basis of a target value depending upon the target value of the position.
Preferably, a member serving as a position reference used in the position measurement performed by the first position measurement system is formed on a structure vibration-isolated from the reference plane.
Alternatively, a member serving as a position reference used in the position measurement performed by the first position measurement system may be formed integrally with the reference plane.
Preferably, a member serving as a position reference used in the position measurement performed by the second position measurement system is formed on a structure vibration-isolated from the reference plane.
Alternatively, a member serving as a position reference used in the position measurement performed by the second position measurement system may be formed integrally with the reference plane.
More preferably, the first movable member and the second movable member are both supported on the reference plane.
Preferably, the second movable member is supported on the reference plane, and the first movable member is supported on the second movable member.
Preferably, the first movable member and the second movable member are movable in directions along two axes parallel to the reference plane.
Preferably, the first movable member is a movable stage, and the second movable member is a stage base or a stator of the first actuator.
Preferably, the first actuator is a linear motor.
According to a second aspect of the present invention, there is provided a stage apparatus including a first movable member movable in a direction parallel to a reference plane; a second movable member movable in a direction parallel to the reference plane; an actuator for generating a force between the first movable member and the second movable member; a fixing mechanism for fixing the second movable member at an arbitrary position within the moving range of the second movable member; a position measurement system for measuring the position of the second movable member; and a control system for controlling the position of the first movable member, using the actuator.
Preferably, the stage apparatus according to the present invention further comprises a controller which positions the first movable member so as to satisfy the following relationship:
Yb=xe2x88x92m/Mxc2x7Ys
where m is the mass of the first movable member, Ys is the target value of the position of the first movable member controlled by the first control system, M is the mass of the the second movable member, and Yb is the target value of the position of the second movable member, wherein the controller releases the second movable member from the fixed state after completion of the positioning of the first movable member.
Preferably, the stage apparatus further comprises a judging unit for judging whether the relationship is satisfied.
If the judging unit judges that the relationship is not satisfied, the controller may again perform the driving to the initial position.
Preferably, a member serving as a position reference used by the position measurement system is formed on a structure vibration-isolated from the reference plane.
Alternatively, a member serving as a position reference used by the position measurement system may be formed integrally with the reference plane.
Preferably, the first movable member and the second movable member are both supported on the reference plane.
More preferably, the second movable member is supported on the reference plane, and the first movable member is supported on the second movable member.
Preferably, the first movable member and the second movable member are movable in directions along two axes parallel to the reference plane.
Preferably, the first movable member is a movable stage, and the second movable member is a stage base or a stator of the first actuator.
Preferably, the first actuator is a linear motor.
According to a third aspect of the present invention, there is provided an exposure apparatus including a first movable member movable in a direction parallel to a reference plane; a second movable member movable in a direction parallel to the reference plane; a first actuator for generating a force between the first movable member and the second movable member; a second actuator for generating a force between the reference plane and the second movable member; a first control system for controlling the position of the first movable member, using the first actuator; and a second control system for controlling the position of the second movable member, using the second actuator in synchronization with the control of the first control system.
According to a fourth aspect of the present invention, there is provided an exposure apparatus including a first movable member movable in a direction parallel to a reference plane; a second movable member movable in a direction parallel to the reference plane; an actuator for generating a force between the first movable member and the second movable member; a fixing mechanism for fixing the second movable member at an arbitrary position within the moving range of the second movable member; a position measurement system for measuring the position of the second movable member; and a control system for controlling the position of the first movable member, using the actuator.
According to a fifth aspect of the present invention, there is provided a method of producing a device, including the steps of preparing an exposure apparatus according to the third aspect of the present invention and performing exposure using the exposure apparatus.
According to a sixth aspect of the present invention, there is provided a method of producing a device, including the steps of preparing an exposure apparatus according to the fourth aspect of the present invention and performing exposure using the exposure apparatus.
Other features and advantages of the present invention will be apparent from the following description taken in conjunction with the accompanying drawings, in which like reference characters designate the same or similar parts throughout the figures thereof.